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Android Build a Simple Android App (2014) Basic Android Programming Initializing a Button

Mahmod Issa
Mahmod Issa
11,745 Points
Posted by Mahmod Issa
Mahmod Issa
11,745 Points

Why cast Button if it is already a type view of Button?

In the textView i should cast the variable because it is not a view type, so why should I cast Button if it is already button?

FunFactsActivity.java 
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class FunFactsActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fun_facts);

        // Declare our View variables and assign them the Views from the layout file
        TextView factLabel = (TextView) findViewById(R.id.factTextView);
        Button showFactButton;
    }
}

1 Answer

Jacob Bergdahl
Jacob Bergdahl
29,119 Points
Jacob Bergdahl
Jacob Bergdahl
29,119 Points

Button and TextView are both children of View. The findViewById() method returns a View. So, if you say something like Button button = findViewById(), it won't work, since a View isn't necessarily a Button (although a Button is always a View). For this reason, you have to cast it.

Mahmod Issa
Mahmod Issa
11,745 Points
Mahmod Issa
Mahmod Issa
11,745 Points

You mean that Button and TextView are subclasses of View?

Jacob Bergdahl
Jacob Bergdahl
29,119 Points
Jacob Bergdahl
Jacob Bergdahl
29,119 Points

Correct! In fact, all widgets, not only Buttons and TextViews, are children of the base class View. ViewGroup is also a subclass of View, and is used for Views that contain other Views, such as LinearLayout and RelativeLayout.